docs: use a shorter SHOW VARIABLES example

[doc-claw-bot]

What is changed, added or deleted? (Required)

• replace the outdated SHOW GLOBAL VARIABLES LIKE 'tidb%' example with a shorter verified SHOW GLOBAL VARIABLES LIKE 'tidb_stmt_summary%' example
• avoid the disputed tidb_wait_split_region_finish row in the example output
• keep the other SQL examples unchanged

Which TiDB version(s) do your changes apply to? (Required)

• master (the latest development version)
• v9.0 (TiDB 9.0 versions)
• v8.5 (TiDB 8.5 versions)
• v8.1 (TiDB 8.1 versions)
• v7.5 (TiDB 7.5 versions)
• v7.1 (TiDB 7.1 versions)
• v6.5 (TiDB 6.5 versions)
• v6.1 (TiDB 6.1 versions)

What is the related PR or file link(s)?

• This PR is translated from: docs: use a shorter SHOW VARIABLES example docs#23176
• Other reference link(s):
  • Verified against a local TiDB v8.5.6 instance for the replacement example query.

Do your changes match any of the following descriptions?

• Delete files
• Change aliases
• Need modification after applied to another branch
• Might cause conflicts after applied to another branch

[ti-chi-bot]

Hi @doc-claw-bot. Thanks for your PR.

I'm waiting for a pingcap member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[pingcap-cla-assistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you all sign our Contributor License Agreement before we can accept your contribution.
1 out of 2 committers have signed the CLA.

✅ qiancai
❌ DocClaw Bot

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2026-07-10 01:38:42.285578716 +0000 UTC m=+332108.321673762: ☑️ agreed by qiancai.

[qiancai]

/ok-to-test

[qiancai]

/approve

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: qiancai

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Needs approval from an approver in each of these files:

• OWNERS [qiancai]

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[doc-claw-bot]

Closing and reopening this translated PR after CLA/account reconfiguration. A replacement PR with the same change will follow shortly.